This invention relates to antennas, phased array antennas, and more specifically to a multi-band phased array antenna.
Satellite communications (SATCOM) systems have been in use for many years for military and commercial applications. New SATCOM systems are requiring multiband operation with both planar and conformal arrays. Specific bands of current military interest include K band GBS (Global Broadcast System)(20 GHz), K/Ka band Wideband Gapfiller (20/30 GHz) and K/Q band MILSTAR/Advanced EHF (20/44 GHz). Commercial SATCOM systems and bands include such systems as Teledesic 29-GHz uplink/19-GHz downlink and Astrolink with 20-GHz downlink/30-GHz uplink.
Military and commercial SATCOM systems require continual connectivity communications for on-the-move vehicles on all frequency bands. This requires a directional lightweight steerable antenna for vehicular mounting. Wide area scan volume coverage and simultaneous beam operation with slaved transmit to receive beams are also required. Circular polarization (CP) is also required by SATCOM systems. LPI/LPD (low probability of interception/low probability of detection) and A/J (antijam) are needed features in military SATCOM systems. A desirable feature in a SATCOM antenna is the ability to provide a beam in the direction of a SATCOM satellite while placing a null in the direction of a potential interfering satellite or a jammer signal.
Previous attempts to solve these SATCOM antenna problems have included passive interlaced arrays where two antenna arrays of some type on different bands are built together or interlaced to reduce size. Interlaced arrays are limited in the number bands of operation and three and four band operation needed for current SATCOM applications is difficult to obtain. Antennas employing reflector technology such parabolic reflectors are difficult to implement in multiple bands. Furthermore, such antennas typically have slow mechanical beam scanning making it difficult to track a communications satellite in a rapidly maneuvering vehicle. Lens antennas are difficult to implement in multiband designs. A three or more band configuration requires different focal points.
A phased array antenna is a beam forming antenna in which the relative phases of the respective signals feeding the antennas are varied such that the effective radiation pattern of the phased array is reinforced in a desired direction and suppressed in undesired directions. The relative amplitudes of constructive and destructive interference effects among the signals radiated by the individual antennas determine the effective radiation pattern of the phased array. A phased array may be used to rapidly electronically scan in azimuth or elevation. Previous phased arrays have been limited in bandwidth. Ultra broadband radiating elements in conventional phased array antennas initiate grating lobes. Efficient broadband radiating elements tend to be large thereby making the entire array too large for many applications. Excessively large radiating element size forces a wide element-to-element spacing within an array, which generates grating lobes at the high end of the bandwidth. Millimeter wave beam steering control and bias distribution networks tend to be very complicated in current phased array antennas. Power generation losses and noise figure corruption occurs due to interconnect losses in conventional phased arrays.
A need exists for a cost effective, lightweight multi-band directional satellite communication antenna based on phased array technology.
A multiband phased array antenna for transmitting and receiving low frequency band signals and high frequency band signals is disclosed. The phased array antenna is assembled from a sub-array of unit cells with the unit cells adjacent to each other. Each unit cell further comprises four walls disposed in a square configuration with parallel pairs of walls and with an open input end and an open radiating end. End-fire radiating elements are located on inner surfaces and on outer surfaces of the four walls for radiating and receiving low frequency band signals out the radiating end. The outer surface end-fire radiating elements serve as inner surface radiating elements for adjacent unit cells. The end-fire radiating elements may be quasi-Yagi radiators or notch radiators such as antipodal notches or Vivaldi notches. Horizontal end-fire radiating elements are disposed on horizontal inner walls to produce a horizontal polarized signal and vertical end-fire radiating elements are disposed on the vertical inner walls to produce a vertical polarized signal. The vertical end-fire radiating elements and the horizontal end-fire radiating elements may be fed in phase quadrature to produce a circular polarized signal.
The unit cell further comprises four or more waveguide radiating elements disposed together in a square configuration. The waveguide radiating elements have open ends for radiating and receiving high frequency band signals through the four walls of the low frequency band radiating elements. The waveguide radiating elements may comprise pairs of triangular waveguides disposed together to form a single square shaped dual band waveguide. The sidewalls of a waveguide may be covered with photonic band gap material to lower the waveguide cutoff frequency.
A plurality of phase shifters are connected to unit cells to shift the phase of the low frequency band signals and the high frequency band signals to steer a beam of the phased array antenna. The phase shifters may comprise MEMS switch-based true time delay phase shifters connected between an RF signal source and the end-fire radiating elements for phase shifting the low frequency signals. The phase shifters may comprise a tunable photonic band gap material in the waveguide radiating element for phase shifting the high frequency signals.
It is an object of the present invention to provide an antenna with multiband operation for commercial and military SATCOM and other applications.
It is an object of the present invention to provide a directional antenna to provide continual communications for rapidly maneuvering vehicles.
It is an advantage of the present invention to provide a phased array antenna having a modular unit cell.
It is an advantage of the present invention to provide an antenna having a compact unit cell with multiband operation.
It is a feature of the present invention to provide simplified phase shifting methods to steer the phased array beam
It is a feature of the present invention to provide a simplified feed system to feed the multiband phased array antenna.